From bb48196715a241375c11fe0aaf23ad7ab912a29d Mon Sep 17 00:00:00 2001
From: Dobrica Pavlinusic <dpavlin@rot13.org>
Date: Fri, 12 Dec 2014 14:13:21 +0100
Subject: [PATCH] added crc implementation

based on code from
http://www.ab-log.ru/smart-house/heating-automation/gaz_meter
---
 dialog.pl | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/dialog.pl b/dialog.pl
index ee20fd1..7daf81c 100755
--- a/dialog.pl
+++ b/dialog.pl
@@ -32,12 +32,32 @@ sub hex2bytes {
 	return $bytes;
 }
 
+sub crc {
+	my $data = shift;
+	my $crc = 0;
+	for my $i ( 0 .. length($data) - 2 ) {
+		if ( $crc & 0x80 ) {
+			$crc = ( $crc << 1 ) ^ 25;
+		} else {
+			$crc = $crc << 1;
+		}
+		$crc = $crc & 0xff;
+		my $byte = ord(substr($data,$i,1));
+		$crc = $crc ^ $byte;
+#		warn "## ", as_hex(chr($byte)), " crc = ", $crc, " ", as_hex(chr($crc));
+	}
+	if ( chr($crc) ne substr($data,-1,1) ) {
+		warn "CRC error for ",as_hex($data), " calulated ", as_hex(chr($crc));
+	}
+}
+
 sub v {
 	my ($hex,$desc) = @_;
 	my $bytes = hex2bytes( $hex );
 	warn "# $desc\n";
 retry:
 	warn ">> ",as_hex( $bytes );
+	crc( $bytes );
 	$port->write( $bytes );
 
 	my $data = $port->read(1);
@@ -46,6 +66,7 @@ retry:
 	goto retry if ord($data) == 0;
 
 	$data .= $port->read(ord($data) - 1);
+	crc($data);
 	warn "<< ",as_hex($data);
 
 }
-- 
2.20.1